1. Field of the Invention
This invention relates generally to implantable leads for conducting electrical signals to and/or from a stimulating pulse generator, and more particularly to neurostimulating leads having electrodes adapted for treatment of neurogenic, neuropathic or neuroceptive nerve conditions.
2. Discussion of the Related Art
Conventional neural stimulation therapies rely on electrode catheters for stimulating various regions of the spinal cord that correspond to each physiologic region of the body. Spinal cord stimulation, however, has limited effectiveness for certain pain conditions primarily due to limited accessibility to targeted nerves. In many cases where spinal cord stimulation is inadequate, spinal or peripheral nerves must be specifically stimulated to provide pain relief. However, with existing technology, nerve specific stimulation can only be accomplished with a surgical implant, which results in scarring and significant patient discomfort. Therefore, a need exists for a lead that provides greater specificity and increased accessibility to perform a broader array of nerve stimulation, while using less invasive methods to improve treatment outcome.
A variety of medical electrode catheters are available today for the diagnosis and treatment of various disorders of the cardiovascular and neurological systems. These electrode catheters can be used to sense electrical activity within the body and to deliver different forms of energy to stimulate, ablate, cauterize or pace. The core electrode technology common to all of these catheter designs is the application of one or more metallic bands on a catheter body. Examples of medical catheters using metallic banded electrodes include permanent and temporary cardiac pacing leads, electrophysiologic (EP) catheters, electrocautery probes and spinal stimulation catheters. The use of pre-formed metallic band electrodes manufactured from noble metals, such as gold or platinum and various other conductive alloys has found widespread application despite their functional design and performance limitations. Metallic band electrodes possess several distinct performance problems. When placed on flexible catheter materials, they add significant stiffness that greatly interferes with the steerability of such catheters. As such, prior art catheters having band electrodes are often restricted to applications where steerability and selective placement are not required. In addition, when DC or RF energy is applied to metallic band electrodes, a thermal field is generated which can interfere with energy delivery, increased power consumption and, in blood environments, create potentially life-threatening blood clots. Finally, the manufacture of catheters utilizing metallic band electrodes is quite labor intensive, resulting in high manufacturing costs.
Placement of leads for both external and implantable RF stimulating devices is quite simple for spinal cord stimulation. Here, a Tuohy needle is inserted into the spinal epidural space and the leads are placed adjacent to the targeted nerves addressing a specific painful region of the body. Relatively high power must be applied when directly stimulating the spinal nerves compared to that required when peripheral nerve stimulation is involved. While this is not a problem when the spinal leads are used with an external stimulator for which battery replacement is relatively easy. It is a major limitation of totally implantable systems in that high power consumption necessarily shortens the time between surgeries for battery replacement. Procedurally, nerve stimulation therapy becomes more challenging when spinal or peripheral nerves of the body are targeted. Due to the fact that many regions of the body cannot be effectively stimulated via the spinal cord, the only alternative in many cases is to surgically implant electrodes. Therefore, a significant need exists for therapeutic access to spinal and peripheral nerves without surgical intervention.
The neurostimulating leads of the present invention eliminate many of the problems encountered with conventional, band-electrode leads. The method employed in fabricating leads of the present invention afford the ability to fabricate highly flexible electrodes on extremely small diameter catheter lead bodies while, if desired, still providing a central lumen permitting such catheters to be advanced over a guidewire or with a stylet until the electrodes disposed thereon are positioned adjacent target tissue.
The present invention provides many improvements and advantages over the related art. The present invention to provides an improved method for fabricating electrical stimulating leads of reduced diameter and carrying a plurality of longitudinally spaced electrodes at the distal end thereof, each of the electrodes being individually connected to a connector at the proximal end thereof by conductors that are embedded within the wall of the lead body and insulated from one another. The present invention provides a method of fabricating such a lead while still maintaining a high degree of steerability thereof. The present invention provides an improved neurostimulating lead having a plurality of longitudinally-spaced, multi-layer, thin film electrodes proximate its distal end, where the electrodes are connected by spiral wound wires embedded in the wall of the lead body and where the lead body can, if desired, retain a central lumen through which a guidewire or stylet may pass. The present invention provides a construction of micro-lead catheters in very small diameters that maximizes inner lumen space for over-the-wire delivery, stylet insertion, infusion of fluids, multi-electrode lead wires and steering systems. The resulting leads provide enhanced sensitivity to low-level signals, providing improved output clarity and lower energy requirements when delivering stimulating currents to selected nerve tissue. Other improvements and advantages over the related art will be evident to those skilled in the art.